The intracellular mechanism responsible for stimulus secretion coupling in the beta cell has been partially delineated. However, the precise roles of the two "second messenger" substances, cyclic 3' 5' adenosine monophosphate (cAMP) and calcium ion are not clear. Experiments have been designed to examine the relevance of cAMP accumulation in isolated islets to the insulin releasing process. Preliminary evidence has indicated that the generation of cAMP in isolated islets may be dependent upon extracellular calcium or the distribution of calcium ion across the cytoplasmic membrane. Information about the effects of calcium ion flux changes on cAMP generation and the effects of cAMP level changes on calcium metabolism are sought. Calcium ion distribution will be perturbed using a calcium antagonist (D600), a divalent cation ionophore (A23187), and a cardiac glycoside (ouabain). Insulin release and cAMP levels will be measured. The effect of high concentrations of glucose on cAMP accumulation in islets exposed to D600 will be measured. Cyclic AMP levels will be altered using alloxan and theophylline. The effect of these manipulations on insulin release will be studied. The ability of the ionophore A23187 to increase islet cAMP levels in alloxan poisoned islets will be observed. An isolated islet perifusion system will be used. The purpose of the proposed study is to better define the relationship between cAMP and calcium ion and to describe their contribution to the control of insulin secretion.